The present invention relates to apparatus and method for measuring vibration of a rotating member and, more particularly, to apparatus and method for measuring vibration of the member when a signal representative of vibration of the member is only available during a portion of a complete revolution of the member and/or is not continuously available during a complete revolution of the member.
It is often desirable to determine vibration of a rotatable member, especially when the member may be subject to vibration due to its physical orientation and/or operating environment. For example, such a member may include a blade, or bucket, of an axial fluid flow turbine which is rigidly secured at a radially inner portion thereof to a shaft and which may be relatively free standing at the radial outer end thereof, so as to form a cantilever configuration.
In one application, the vibratory pattern of the member may be used to develop a "signature" of the machine. That is, the vibratory pattern of the member may be determined during normal operating conditions upon initial installation of the machine or at some other desired time. Periodic or continual monitoring of the vibratory pattern of the member, after establishment of the signature, may detect a change in the pattern, which through operating history and comparative similar changes of like members, may be determined to be indicative of a particular abnormal operating condition of the machine and/or member. Such changes in vibratory pattern may be able to be detected well before other more debilitating or detrimental physical events are manifested by the machine. For example, a change in the vibratory pattern of a member may provide an early indication of problems associated with the bearings and/or support foundation of the machine. In addition, excessive vibration of a member may result in fatigue which if continued over a sustained period of time may cause cracking and/or rupture of the member.
One such apparatus for monitoring vibration of a blade of an axial flow compressor or turbine is described in U.S. Pat. No. 3,208,269--Eccles et al. The apparatus of the U.S. Pat. No. 3,208,269 shows an electrical conductor of a generally zigzag shape, substantially totally circumferentially surrounding the path described by the outer portion of the blade. Further, to monitor vibration of a plurality of blades using the teachings of the U.S. Pat. No. 3,208,269, it is necessary to use at least as many axially spaced apart zigzag conductors as the number of blades to be monitored. This results in using more space than may be available for deploying the multiple zigzag conductors and further requires substantially increased care when positioning the zigzag conductors in order to ensure that the branches of the conductors are equally circumferentially spaced about the radial outer extremity of the blades. In addition, axial expansion of the shaft during operation necessitates that the conductors be accurately axially spaced. Unequal circumferential spacing between branches of the conductors will result in an undesirable modulation of the carrier signal to be generated in the conductors, which will ultimately be detected as a vibration, while improper axial spacing may result in a magnet influencing the wrong conductor. Further, it may not be desirable or feasible to entirely circumferentially surround the blades with a zigzag conductor, such as when the housing surrounding the blades is segmented.
Accordingly, it is an object of the present invention to provide means and method for monitoring one or more rotating members without having to use a respective axially spaced apart zigzag conductor for each member being monitored.
Another object of the present invention is to provide means and method for monitoring a rotating member without need to totally circumferentially surround the member with a conductor.